System for reducing stress induced effects during determination of fluid optical constants

ABSTRACT

A system for determination of optical constants of liquids, including provision for reducing stress induced effects while obtaining data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of application Ser. No.11/098,669 Filed Apr. 2, 2005 now U.S. Pat. No. 7,239,391; and thereviaof Allowed application Ser. No. 10/238,241 Filed Sep. 10, 2002, (nowU.S. Pat. No. 6,937,341); and therevia of application Ser. No.09/756,515 Filed Jan. 9, 2001, (now U.S. Pat. No. 6,455,853) andtherevia Claims benefit of Provisional Application Ser. No. 60/183,977Filed Feb. 22, 2000. This application further Claims Benefit ofProvisional Application Ser. No. 60/318,518, Filed Sep. 10, 2001 viaapplication Ser. No. 10/238,241. This application directly Claimsbenefit of Provisional Application Ser. No. 60/623,633, Filed Nov. 1,2004.

TECHNICAL FIELD

The disclosed invention relates to systems for use in investigatingoptical properties of materials, and more particularly to a system forreducing stress induced effects during determination of opticalconstants of liquids which is well suited for use in polarimeter,ellipsometer and the like systems with wavelengths in VUV, UV, Visible,Infrared, Far Infrared, and Radio ranges.

BACKGROUND

As disclosed in Co-pending Allowed application Ser. No. 10/238,241, thecharacterization of fluid samples, such as biological samples, isincreasing in importance. Further, it is known to investigate a sampleplaced on a first surface of a sample stage element, which sample stageelement presents with first and second, typically, but not necessarilysubstantially parallel surfaces, by utilizing an electromagnetic beamapplied from said first surface side of said sample stage element suchthat said beam reflects from said sample into a detector. It is furtherknown to independently investigate a sample placed on a sample stageelement first surface utilizing an electromagnetic beam applied from asecond, oppositely facing surface side of said sample stage element suchthat said beam reflects from the sample into a detector. Of course thesample stage element must be transparent to said electromagneticradiation applied from the second surface side thereof in order toaccess the sample. Further, it is to be understood that electromagneticradiation can be of any functional wavelength, either monochromatic,(ie. laser source), or spectroscopic.

The primary motivation for the disclosed invention is found in a need todo more definitive assays and analysis in areas such as:

-   -   antibody/antigen interactions;    -   microbiology (eg. viruses, toxins etc.);    -   physiological (eg. hormones);    -   drugs (therapeutic and illegal).        In addition, the present invention finds application in        fundamental science where, for instance, bonding mechanisms and        attachment rates for proteins and/or DNA to surfaces and other        biomaterials are of interest, as well as the dielectric        functions of bulk fluids.

The application of Spectroscopic Ellipsometry (SE) to biologics providesutility because reflectance from Bio-films on opaque substrates isdifficult to detect where intensity changes are small. In additionSurface Plasmon Resonance (SPR), while sensitive, has a limited spectralrange and can be applied only to limited types of substrate materialsand layer thicknesses.

It is noted that a suitable system for investigating biologics must berelatively immune to such as temperature sensitive birefringence ofelectromagnetic wavelength windows, which requires careful design andmounting. And, while not related to measurement apparatus, temperaturesensitivity of reagents and reactions and reagent concentrationsensitivity can enter artifacts into results, hence a suitable systemfor investigating biologics must provide means to minimize randomeffects therein. A robust system and method therefore should providecompensation capability, at least to compensate the identifiedbirefringence, during data in analysis.

Another source of birefringence is pressure applied to a system to holdelements in place with respect to one another.

Continuing, while the herein disclosed invention can be used in anymaterial system investigation system such as Polarimeter, Reflectometer,Spectrophotometer and the like Systems, an important application is withEllipsometer Systems, whether monochromatic or spectroscopic. It shouldtherefore be understood that Ellipsometry involves acquisition of samplesystem characterizing data at single or multiple Wavelengths, and/or atone or more Angle(s)-of-Incidence (AOI) of a Beam of ElectromagneticRadiation to a surface of the sample system. Ellipsometry is generallywell described in a great many publication, one such publication being areview paper by Collins, titled “Automatic Rotating ElementEllipsometers: Calibration, Operation and Real-Time Applications”, Rev.Sci. Instrum., 61(8) (1990).

A typical goal in ellipsometry is to obtain, for each wavelength in, andangle of incidence of said beam of electromagnetic radiation caused tointeract with a sample system, sample system characterizing PSI andDELTA values, where PSI is related to a change in a ratio of magnitudesof orthogonal components r_(p)/r_(s) in said beam of electromagneticradiation, and wherein DELTA is related to a phase shift entered betweensaid orthogonal components r_(p) and r_(s), caused by interaction withsaid sample system. This is expressed by:TAN(ψ)e ^(i(Δ)) =r _(s) /r _(p).(Note the availability of the phase DELTA (Δ) data is a distinguishingfactor between ellipsometry and reflectometry).

Continuing, Ellipsometer Systems generally include a source of a beam ofelectromagnetic radiation, a Polarizer, which serves to impose a stateof polarization on a beam of electromagnetic radiation, a Stage forsupporting a sample system, and an Analyzer which serves to select apolarization state in a beam of electromagnetic radiation after it hasinteracted with a material system, and passed it to a Detector Systemfor analysis therein. As well, one or more Compensator(s) can be presentand serve to affect a phase angle between orthogonal components of apolarized beam of electromagnetic radiation. A number of types ofellipsometer systems exist, such as those which include rotatingelements and those which include modulation elements. Those includingrotating elements include Rotating Polarizer (RP), Rotating Analyzer(RA) and Rotating Compensator (RC). A preferred embodiment is a RotatingCompensator Ellipsometer System because, it is noted, RotatingCompensator Ellipsometer Systems do not demonstrate “Dead-Spots” whereobtaining data is difficult. They can read PSI and DELTA of a MaterialSystem over a full Range of Degrees with the only limitation being thatif PSI becomes essentially zero (0.0), DELTA can not then be determinedas there is not sufficient PSI Polar Vector Length to form the anglebetween the PSI Vector and an “X” axis. In comparison, Rotating Analyzerand Rotating Polarizer Ellipsometers have “Dead Spots” at DELTA's near0.0 or 180 Degrees and Modulation Element Ellipsometers also have “DeadSpots” at PSI near 45 Degrees). The utility of Rotating CompensatorEllipsometer Systems should then be apparent. Another benefit providedby fixed Polarizer (P) and Analyzer (A) positions is that polarizationstate sensitivity to input and output optics during data acquisition isessentially non-existent. This enables relatively easy use of opticfibers, mirrors, lenses etc. for input/output.

Further, it is to be understood that causing a polarized beam ofelectromagnetic radiation to interact with a sample system generallycauses change in the ratio of the intensities of orthogonal componentsthereof and/or the phase angle between said orthogonal components. Thesame is generally true for interaction between any system component anda polarized beam of electromagnetic radiation. In recognition of theneed to isolate the effects of an investigated sample system from thosecaused by interaction between a beam of electromagnetic radiation andsystem components other than said sample system, (to enable accuratecharacterization of a sample system per se.), this Specificationincorporates by reference the regression procedure of U.S. Pat. No.5,872,630 to Johs et al. in that it describes simultaneous evaluation ofsample characterizing parameters such as PSI and DELTA, as well systemcharacterizing parameters, and this Specification also incorporates byreference the Vacuum Chamber Window Correction methodology of U.S. Pat.No. 6,034,777 to Johs et al. to account for phase shifts entered betweenorthogonal components of a beam of electromagnetic radiation, bydisclosed invention system windows and/or beam entry elements.

A Published patent application of which the Applicants are aware is US2002/0024668 by Stehle et al. This application discloses the use of twoelectromagnetic beams applied orthogonally to a sample, and oneelectromagnetic beam applied normally thereto through effective windowswhich are oriented parallel to the surface of the sample.

Other patents of which the Inventor is aware include U.S. Pat. No.5,757,494 to Green et al., in which is taught a method for extending therange of Rotating Analyzer/Polarizer ellipsometer systems to allowmeasurement of DELTA'S near zero (0.0) and one-hundred-eighty (180)degrees. Said patent describes the presence of a window-like variablebirefringent components which is added to a Rotating Analyzer/Polarizerellipsometer system, and the application thereof during dataacquisition, to enable the identified capability.

A patent to Thompson et al. U.S. Pat. No. 5,706,212 teaches amathematical regression based double Fourier series ellipsometercalibration procedure for application, primarily, in calibratingellipsometers system utilized in infrared wavelength range. Birefringentwindow-like compensators are described as present in the system thereof,and discussion of correlation of retardations entered by sequentiallyadjacent elements which do not rotate with respect to one another duringdata acquisition is described therein.

A patent to Woollam et al, U.S. Pat. No. 5,582,646 is disclosed as itdescribes obtaining ellipsometric data through windows in a vacuumchamber, utilizing other than a Brewster Angle of Incidence.

Patent to Woollam et al, U.S. Pat. No. 5,373,359, patent to Johs et al.U.S. Pat. No. 5,666,201 and patent to Green et al., U.S. Pat. No.5,521,706, and patent to Johs et al., U.S. Pat. No. 5,504,582 aredisclosed for general information as they pertain to Rotating Analyzerellipsometer systems.

Patent to Bernoux et al., U.S. Pat. No. 5,329,357 is identified as itdescribes the use of optical fibers as input and output means in anellipsometer system.

U.S. Pat. No. 5,991,048 To Karlson et al. describes a system forpracticing Surface Plasmon Resonance in which a light pipe arrangementis present upon which can be situated a flow cell. Sample entered to theflow cell becomes situated on the upper surface of the light pipe andlight entered to the light pipe interacts with it from below, thenexists and enters a multi-element detector at various angles.

U.S. Pat. No. 6,316,274 B1 to Herron et al. describes a single lightsource system for practicing multi-analyte homogeneousflouro-immunoassays, via detecting of reflected and transmitted beams.

U.S. Pat. No. 5,313,264 to Ivarsson et al. describes a single lightsource system in which a light beam accesses a sample via a prism,(which can be semicircular in shape), and reflects into a detector.

U.S. Pat. No. 4,159,874 to Dearth et al. describes another single lightsource system which includes upper and lower sensors.

U.S. Pat. No. 6,200,814 B1 to Malmquist et al. describes a method andsystem for providing laminar flow over one or more discrete sensingareas.

U.S. Pat. No. 4,076,420 to De Maeyer et al. describes a system forinvestigating fast chemical reactions by optical detection of, forinstance, absorption or fluorescence or scattered light, includingdetection of polarized light.

Patents identified during the preparation and prosecution of Pendingapplication Ser. No. 09/756,515, from which this Application is a CIPare:

U.S. Pat. No. 5,625,455 to Nash et al.;

U.S. Pat. No. 5,486,701 to Norton et al.;

U.S. Pat. No. 5,900,633 to Solomon et al.;

U.S. Pat. No. 4,807,994 to Felch et al.;

U.S. Pat. No. 4,472,633 to Motooka;

U.S. Pat. No. 6,049,220 to Borden et al.

U.S. Pat. No. 6,738,139 to Synowicki is disclosed as it describesdetermining optical constants of fluids using thin films thereof.

Scientific Articles are also identified as follows:

“Determination of the mid-IR optical Constants of Water and LubricantsUsing IR Ellipsometry Combined with ATR an Cell” Tiwald et al., ThinSolids Films, 313-314 (1998).

An article by Johs, titled “Regression Calibration Method For RotatingElement Ellipsometers”, which appeared in Thin Film Solids, Vol. 234 in1993 is also identified as it describes an approach to ellipsometercalibration.

Another paper, by Straaher et al., titled “The Influence of Cell WindowImperfections on the Calibration and Measured Data of Two Types ofRotating Analyzer Ellipsometers”, Surface Sci., North Holland, 96,(1980), describes a graphical method for determining a plane ofincidence in the presence of windows with small retardation.

An article by Collins titled “Automated Rotating Element Ellipsometers:Calibration, Operation, and Real-Time Applications”, Rev. Sci. Instrum.61(8), August 1990 is disclosed for the general insight to ellipsometersystems it provides.

An article by Kleim et al. titled “Systematic Errors inRotating-Compensator Ellipsometry” published in J. Opt. Soc. Am./Vol.11, No. 9, September 1994 is identified as it describes calibration ofrotating compensator ellipsometers.

An Article by An and Collins titled “Waveform Analysis With OpticalMultichannel Detectors: Applications for Rapid-Scan SpectroscopicEllipsometer”, Rev. Sci. Instrum., 62 (8), August 1991 is alsoidentified as it discusses effects such as Detection System ErrorCharacterization, Stray Light, Image Persistence etc., and calibrationthereof.

A paper which is co-authored by an inventor herein is titled “In SituMulti-Wavelength Ellipsometric Control of Thickness and Composition ofBragg Reflector Structures”, by Herzinger, Johs, Reich, Carpenter & VanHove, Mat. Res. Soc. Symp. Proc., Vol. 406, (1996) is also disclosed.

A paper by Nijs & Silfhout, titled “Systematic and Random Errors inRotating-Analyzer Ellipsometry”, J. Opt. Soc. Am. A., Vol. 5, No. 6,(June 1988) is also identified.

An article by Jellison Jr. titled “Data Analysis for SpectroscopicEllipsometry”, Thin Film Solids, 234, (1993) is also disclosed.

Papers of interest in the area by Azzam & Bashara;

-   -   “Unified Analysis of Ellipsometry Errors Due to Imperfect        Components Cell-Window Birefringence, and Incorrect Azimuth        Angles”, J. of the Opt. Soc. Am., Vol 61, No. 5, (May 1971);    -   “Analysis of Systematic Errors in Rotating-Analyzer        Ellipsometers”, J. of the Opt. Soc. Am., Vol. 64, No. 11,        (November 1974).

An unpublished article by Poksinski et al. titled “Total InternalReflection Ellipsometry”, describes application of total internalreflection to investigate protein using ellipsometric techniques.

Further identified is a flyer from Harrick, titled “InternalReflection/ATR”.

It is also mentioned that a book by Azzam and Bashara titled“Ellipsometry and Polarized light” North-Holland, 1977 is disclosed andincorporated herein by reference for general theory, as is a book whichis authority regarding mathematical regression, (ie. a book titledNumerical Recipes in “C”, 1988, Cambridge University Press.

Continuing, it is known to place a prism comprising 1st, 2nd and 3rdsides, atop of a material and direct electromagnetic radiation along aperpendicular to the 1st side thereof so that it totally internallyreflects from the 2nd surface thereof, then exits via the 3rd sidethereof. It is also known to place such a prism atop a liquid containingsystem, and apply sufficient pressure to said prism to effect goodcontact between said prism's 2nd side and said liquid, while applyingelectromagnetic radiation, as just described, to investigate opticalproperties of said liquid. A problem, arises, however, in that applyingpressure to the prism causes it to introduce stress induced effects intoobtained data.

It is also known to mount systems to be analyzed by electromagneticradiation on vertically oriented stages such that the surface of asample to be investigated faces laterally. When a vertical mounting isutilized, however, to monitor liquids, some means for containing liquidis necessary.

In view of the foregoing, a system was disclosed in application Ser. No.10/238,241, Filed Sep. 10, 2002, for enabling substantially simultaneousinvestigation of a fluid sample with at least two electromagneticradiation beams comprises a sample stage element having a first surface,and a second surface, typically, but not necessarily substantiallyparallel to said first surface. Said system further comprises a celladjacent to said first sample stage element surface which comprises:

-   -   input and output windows;    -   input and output means for entering and exiting fluid sample;    -   an internal volume which is substantially closed but which has        an opening adjacent to said sample stage element first surface        such that fluid sample entered into said cell via said input        means can access said adjacent sample stage surface. Said system        further comprises a beam entry element in functional combination        with said sample stage element second surface.

In use fluid sample is entered to said cell through said input means forentering fluid sample, and one electromagnetic radiation beam is enteredthrough said input window of said cell which is adjacent to one surfaceof the sample stage element, and a second electromagnetic radiation beamis entered through said beam entry element adjacent to said sample stageelement second surface. All entering and exiting electromagneticradiation preferably enters and exits through window or beam entryelement surfaces which are oriented substantially normal to the locusthereof.

It is noted that the beam entry element through which said secondelectromagnetic radiation beam is entered is preferably of a shapeselected from the group consisting of:

-   -   prism;    -   half-spherical; and    -   half-cylinder;        and made of a material with is substantially transparent to said        second beam contained wavelengths.

In addition, the cell can be separated from said sample stage firstsurface by gasket or “O” ring means or the like, such that fluid sampleentered into said cell becomes present within said gasket or “O” ringmeans or the like on said sample stage first surface.

It should also be understood that at least two elements selected fromthe group:

-   -   sample stage element;    -   cell; and    -   beam entry element;        can be integrated into one another. For instance, the cell can        be continuous with the first surface of the sample stage        element, and/or the sample stage element and the beam entry        element can be of a continuous construction.

An “integrated” system for enabling substantially simultaneousinvestigation of a fluid sample with at least two electromagneticradiation beams can then be described as comprising a cell witheffective input and output windows; input and output means for enteringand exiting fluid sample and an internal volume, said integrated systemfurther comprising a beam entry element in functional combination withsaid cell, and located therebelow, as the integrated system is viewed inupright side elevation. In use fluid sample is entered to said cellthrough said input means for entering fluid sample, and oneelectromagnetic radiation beam is entered through said effective inputwindow of said cell, and a second electromagnetic radiation beam isentered through said beam entry element. As before, all entering andexiting electromagnetic radiation preferably enters and exits througheffective cell window or beam entry element surface(s) which areoriented substantially normal to the locus thereof. And, again, theeffective input and output windows and the beam entry element, throughwhich electromagnetic radiation beams are passed can be of a shapeselected from the group consisting of:

-   -   prism;    -   half-spherical; and    -   half-cylinder.        The input and output windows can also be of separate        construction. Further, in one variation the cell and beam entry        element are of continuous construction.

Another recitation of a presently disclosed system for enablingsubstantially simultaneous investigation of a fluid sample with at leasttwo electromagnetic radiation beams provides that said system comprise acell, which cell comprises:

effective input and output windows;

input and output means for entering and exiting fluid sample;

an internal volume presenting with a surface therewithin.

Said system further comprises a beam entry element in functionalcombination with said cell, and being located, as viewed in upright sideelevation, below said surface within said cell. In use fluid sample isentered to the internal volume of said cell through said input means forentering fluid sample, and one electromagnetic radiation beam is enteredthrough said effective input window of said cell, and a secondelectromagnetic radiation beam is entered through said beam entryelement, to the end that both said first and second electromagneticbeams interact, at the same or different magnitude oblique angles withrespect to said surface in said internal volume of said cell, with saidfluid sample present on said surface, and then exit and enter detectormeans.

Further, in any embodiment, the cell can also comprise a third windowand a third electromagnetic beam can be caused to enter said internalvolume therethrough at a substantially normal angle of incidence to saidsurface within said internal volume, transmit through, (or reflectfrom), said sample caused to be present on said surface, and enter adetector. Typically such a third beam will not be subject to having apolarization state imposed thereupon and is utilized to determineintensity attenuation resulting from interaction, (transmission orreflection via beam splitter), with said sample.

Note that the terminology “effective” input and output windows ispresent to indicate that said windows can be locations on such as aprism shaped, half-spherical shaped or half-cylinder shaped element,although a typical cell has physically separate input and outputwindows, and possibly a third window mounted therewithin.

Also a method of investigating fluid sample with at least two beams ofelectromagnetic radiation was proposed in application Ser. No.10/238,241, that comprises the steps of:

a. providing a system as described above;

b. entering fluid sample into said cell internal volume so that itcontacts said surface therewithin;

c. causing a first beam of electromagnetic radiation to, at an obliqueangle, approach said sample directly, (not through said stage); and

d. causing a second beam of electromagnetic radiation to approach, at anoblique angle, said sample through said “stage” upon which it issupported.

Reflected components of each of the at least two electromagnetic beamsare detected by one or more detector(s) and analyzed. (Single ormultiple detector systems can be utilized). Particularly, but notexclusively, where a single detector system is used fiber optics can beused to guide electromagnetic radiation into different detector elementsthereof.

It should also be appreciated that data is obtained from both “sides” ofa sample present on said “stage” surface inside said cell internalvolume. Use of the effective two data sets acquired as described in asimultaneous regression allows better determination of sampleproperties, such as uncorrelated thickness and refractive index.

Another invention method disclosed in the 241 application, ofsimultaneously investigating sample with at least two beams ofelectromagnetic radiation, comprises the steps of:

a. providing a system for enabling substantially simultaneousinvestigation of a fluid sample with at least two electromagneticradiation beams, said system comprising a sample stage which has firstand effective second surface sides;

such that in use one electromagnetic radiation beam is entered from thefirst surface side of said sample stage, and a second electromagneticradiation beam is entered from the effective second surface side of saidsample stage, each at an oblique angle thereto;

b. providing a sample on said first surface of said sample stage;

c. causing a first beam of electromagnetic radiation to approach saidsample on said first surface from the first surface side of said samplestage; and

d. substantially simultaneously with step c. causing a second beam ofelectromagnetic radiation to approach said sample on said first surfaceof the sample stage from the second effective surface side of saidsample stage.

It is noted that the terminology “substantially simultaneously” is to beinterpreted to include per se. simultaneous and at times separated byshort delays, (eg. milli-seconds to seconds or longer).

It is also noted that the terminology “effective” second surface is usedto indicate that said “effective” second surface need not be parallel tothe first surface upon which is caused to be present sample. Inparticular an “effective” second surface can be a perimeter surface of aprism, half-spherical or half-cylinder shaped beam entry element whichis affixed to a cell, said beam entry element forming what might betermed a base to said cell.

Further, it should be appreciated that two electromagnetic beams can beof similar or different polarization states, wavelength content, can beapplied at the same or different angles-of-incidence to a sample on theinternal surface of the cell, and can be substantially simultaneouslyapplied by elements of one, or more than one, ellipsometer system(s).For instance, a source of electromagnetic radiation can be configured toprovide two beams, one beam being applied from the one side, and onefrom the other side of a sample stage. The two beams can be, forinstance, guided via optical fibers from one or more than one sources.And, reflected beams can be caused to enter different detectors or thesame detector, (eg. as directed by optical fibers).

A preferred 241 application embodiment provided that an electromagneticbeam directed toward one side of a sample stage surface be comprised ofwavelength content which differs from that of a second beam ofelectromagnetic radiation directed to enter from the other of saidsample stage surface. Another preferred embodiment provides that the twoelectromagnetic beams have similar, or different, wavelength contentsbut are directed toward the sample stage surface at different obliqueangles-of-incidence, (one from above and one from below the sample stageas the system is viewed in elevation). Another preferred embodimentprovides that the two electromagnetic beams have similar, or differentpolarization states imposed thereupon.

It is specifically noted that the first and/or second electromagneticbeams mentioned above can be provided by a selection from the groupconsisting of:

-   -   ellipsometer;    -   polarimeter;        which monitor changes in both the ratio of magnitudes of        orthogonal components of an electromagnetic beam and the phase        angle therebetween, as a result of interaction with a sample; or        by a selection from the group consisting of:    -   reflectometer; and    -   spectrophotometer;        which monitor change in intensity before and after interaction        with a sample, although the later selections are not as relevant        because birefringence of materials in intensity measurements is        not typically a critical factor.

It is emphasized that the foregoing disclosed application ofellipsometric beams to, at oblique angles of incidence, investigate asample from two sides thereof. It is again noted that a thirdelectromagnetic beam, (eg. an unpolarized intensity beam), can beapplied substantially normal to the effective surface upon which ispresent a fluid sample to enable acquiring beam attenuation transmissiondata, and said data can also be used in sample analysis.

U.S. Pat. No. 5,872,630 methodology for calibration of an ellipsometer,and U.S. Pat. No. 6,034,777 methodology for breaking correlation betweenthe effects of the input and output windows and a sample beinginvestigated, which methodology was recited in the Background Section,can of course be added to the preceding recitations to provide morecomplete methodology.

The beam entry element can be made of ZnSe, Ge or Si, (with specifictradename examples being KRS-5, and INTRAN), to provide Infraredtransparency, with the cell windows being transparent to UV, Visible andNear Infrared.

A need exists for a system which contains a liquid in a cavity whiledata is obtained by applying electromagnetic radiation through a prismaffixed thereto, to investigate optical properties of said liquid,wherein the system comprises a means for affixing said prism withoutinducing birefringence causing stress therein.

DISCLOSURE OF THE INVENTION

The disclosed invention is a system and method for reducing stress inoptical elements used to receive electromagnetic radiation, direct it toa sample, and then mediate its receipt by a detector. For instance, theoptical element might be pyramid shaped and applied to allow monitoringliquid adjacent to a side thereof which is caused to be in contact withthe liquid. Common practice is to secure the optical element in positionby applying force to an apex thereof which is opposite said side thereofin contact with said liquid. The present invention system comprises anadditional element to which force can be applied instead of said apex.

An embodiment of the disclosed invention is a system for use ininvestigating optical properties of a liquid comprising:

-   -   a prism element comprising first, second and third substantially        flat sides, the second side of which is extended laterally        beyond projected meeting points with the first and third sides;    -   a second element comprising closed sides and top and an open        bottom.        The laterally extended second side of said prism is placed into        functional contact with said second element at the bottom        thereof to form a liquid containing cavity, such that leakage of        liquid which is caused to be present in said liquid containing        cavity does not occur through said contact point. In use liquid        is caused to be present in said liquid containing cavity and        electromagnetic radiation is caused to enter said first or third        side of said prism, interact with said second side thereof, and        totally internally reflect through said third or first side        thereof, respectively.

A modified present invention system for use in investigating opticalproperties of a liquid comprises:

a prism comprising first, second and third sides;

an intermediate element;

a third element comprising closed sides and top and an open bottom;

wherein said second side of said prism is affixed to said intermediateelement by substantially stress free means, and

wherein said intermediate element when placed into contact with thebottom of said third element forms a liquid containing cavity, saidthird element and intermediate element being forced into functionalcontact with one another such that leakage of liquid caused to bepresent in said liquid containing cavity does not occur through saidcontact point. In use liquid can be caused to be present in said liquidcontaining cavity and electromagnetic radiation can be caused to entersaid first or third side of said prism, interact with said second sidethereof, totally internally reflect and exit through said third or firstside thereof.

The disclosed invention is a system and method for reducing stress inoptical elements used to receive electromagnetic radiation, direct it toa sample and then mediate its receipt by a detector. For instance, theoptical element might be pyramid shaped and applied to allow monitoringliquid adjacent to a side thereof, with common practice being to secureit in position by applying force to an apex thereof which is oppositesaid side. The present invention system comprises an additional elementto which force can be applied instead of said apex. Said intermediateelement can comprise a cavity sequestered within said intermediateelement, and said cavity can be filled with a fluid. Alternatively, sucha cavity in the intermediate element can be continuous with the liquidcontaining cavity of the third element. Another embodiment provides thatthe prism and intermediate element are of single piece construction.

A variation of the system for use in investigating optical properties ofa liquid comprises:

-   -   a half sphere or half cylinder element comprising a first curved        and second substantially flat side, the second side of which is        extended laterally beyond the points of intersection with the        first curved side;    -   a second element comprising closed sides and top and an open        bottom;        the laterally extended second side of said half sphere or half        cylinder being placed into functional contact with said second        element at the bottom thereof to form a liquid containing        cavity; such that leakage of liquid which is caused to be        present in said liquid containing cavity does not occur through        said contact point;        such that in use liquid is caused to be present in said liquid        containing cavity and electromagnetic radiation is caused to        enter said first curved side of said half sphere or half        cylinder, interact with said second side thereof, and totally        internally reflect through said first curved side of said half        sphere or half cylinder, respectively.

Another variation of the present invention system for use ininvestigating optical properties of a liquid comprises:

a half sphere or half cylinder comprising first curved and secondsubstantially flat side;

an intermediate element;

a third element comprising closed sides and top and an open bottom;

wherein said second substantially flat side of said half sphere isaffixed to said intermediate element by substantially stress free means,and wherein said intermediate element when placed into contact with thebottom of said third element forms a liquid containing cavity, saidthird element and intermediate element being forced into functionalcontact with one another such that leakage of liquid caused to bepresent in said liquid containing cavity does not occur through saidcontact point;such that in use liquid can be caused to be present in said liquidcontaining cavity and electromagnetic radiation can be caused to entersaid first side of said half sphere or half cylinder, interact with saidsecond substantially flat side thereof, totally internally reflect andexit through said first half sphere or half cylinder first side thereof.

It is noted that the foregoing description described the presentinvention system as viewed in elevation with one element thereof havingan open “bottom”. It is to be understood that the system can be rotatedto orient the open “bottom” so that it faces other than downward andremain within the scope of the invention.

A present invention method of determining the optical properties of aliquid comprising the steps of:

a) providing a system for use in investigating optical properties of aliquid comprising a selection from the group consisting of:

-   -   a prism element comprising first, second and third substantially        flat sides, the second side of which is extended laterally        beyond projected meeting points with the first and third sides;        and    -   a half sphere or half cylinder element comprising a first curved        and second substantially flat side, the second side of which is        extended laterally beyond the points of intersection of first        curved side;    -   said system further comprising a second element comprising        closed sides and top and an open bottom;        the laterally extended second side of said prism, half sphere or        half cylinder element being placed into functional contact with        said second element at the bottom thereof to form a liquid        containing cavity, such that leakage of liquid which is caused        to be present in said liquid containing cavity does not occur        through said contact point;        such that in use liquid can be caused to be present in said        liquid containing cavity and electromagnetic radiation can be        caused to enter said first curved side of said half sphere or        half cylinder element, or enter said first or third side of said        prism, interact with said second substantially flat side of said        half sphere or half cylinder element or said prism, totally        internally reflect therefrom and exit through said first curved        side of said half sphere or half cylinder element or said third        or first side thereof, respectively;

b) causing said liquid containing cavity to contain a liquid;

c) causing electromagnetic radiation to enter said first curved side ofsaid half sphere or half cylinder element or enter said first or thirdside of said prism, interact with said substantially flat second sidethereof, totally internally reflect and exit through said curved side ofsaid half sphere or half cylinder element or said third or first sidethereof respectively and enter a detector;

d) analyzing data provided by the detector in response to theelectromagnetic radiation that enters thereinto to the end that opticalproperties of the liquid are determined.

Said method can involve application of a system involving anintermediate element that extends laterally beyond projected meetingpoints with the first and third sides, or laterally beyond the points ofintersection of first curved side, to which said prism, half sphere orhalf cylinder element is affixed; or the prism, half sphere or halfcylinder element and intermediate element can be merged into a singlecontinuous element.An additional step can comprise rotating the system to orient the open“bottom” so that it faces other than downward.

The present invention will be better understood by reference to theDetailed Description in conjunction with the Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows Prior Art wherein a Liquid (L) containing Cavity is forcedagainst a Prism (P) by applying Force (F) to said Prism.

FIGS. 2-4 shows present invention systems for reducing the effects offorces applied to keep system elements in contact with one another,demonstrating both prism (solid lines) and half sphere or half cylinder(dashed lines), shaped elements.

FIG. 5 demonstrates an ellipsometer system.

DETAILED DESCRIPTION

Turning now to the Drawings, FIG. 1 shows Prior Art wherein a Liquid (L)containing Cavity is forced against a Prism (P) by applying Force (F) tosaid Prism. Said Force (F) can cause stress in the Prism and induceartifacts to data obtained by causing electromagnetic radiation to passthrough said Prism (P), interact with the Prism (P)-Liquid (L)interface, and exit said Prism (P).

FIG. 2 shows a present invention system for use in investigating opticalproperties of a liquid comprising:

-   -   a prism (P) element comprising first (1st), second (2nd) and        third (3rd) substantially flat sides, the second (2nd) side of        which is extended laterally beyond projected meeting points with        the first 1st and third (3rd) sides;    -   a second (2) element comprising closed sides and top and an open        bottom;        the extended second (2nd) side of said prism (P) being placed        into functional contact with said second (2) element at the        bottom thereof, typically via at least one gasket or “O” ring or        the like means to provide a seal to fluid, to form a liquid (L)        containing cavity (2C); such that leakage of liquid which is        caused to be present in said liquid containing cavity does not        occur through said contact point;        such that in use liquid (L) can be caused to be present in said        liquid (L) containing cavity (2C) and electromagnetic radiation        can be caused to enter said first (1st) or third (3rd) side of        said prism (P), interact with said second (2nd) side thereof,        and totally internally reflect through said third (3rd) or first        (1st) side thereof, respectively.

FIG. 3 shows a system for use in investigating optical properties of aliquid comprising:

a prism comprising first (1st), second (2nd) and third (3rd)substantially flat sides;

an intermediate element (IE);

a third (3) element comprising closed sides and top and an open bottom;

wherein said second (2nd) side of said prism (P) is affixed to saidintermediate element (IE) by substantially stress free means, andwherein said intermediate element (IE) when placed into functionalcontact with the bottom of said third (3) element forms a liquid (L)containing cavity (3C), said third (3) element and intermediate element(IE) being forced into contact with one another such that leakage ofliquid (L) caused to be present in said liquid containing cavity (3C)does not occur through said contact point;such that in use liquid can be caused to be present in said liquidcontaining cavity (3C) and electromagnetic radiation can be caused toenter said first (1st) or third (3rd) side of said prism (P), interactwith said second (2nd) side thereof, totally internally reflect and exitthrough said third (3rd) or first (1st) side thereof.

As shown, said intermediate element (IE) can comprise a cavity (C)sequestered therewithin, and said cavity (C), when present, can befilled with a fluid, such as the liquid (L). Alternatively, such acavity (C) in the intermediate element (IE) can be continuous with theliquid (L) containing cavity (C) of the third (3) element. Further, itis noted that the interface between the prism (P) and the intermediateelement (IE) can have an index of refraction matching liquid presenttherewithin.

It is noted that the FIG. 2 system results from the FIG. 3 system if asolid, (eg. no cavity (C) present therein), intermediate element (IE) isphysically merged with the prism (P). When present, the cavity (C) ofthe intermediate element (IE) can be continuous with, via a pathway(PW), said liquid containing cavity (3C) of the third element (3), sothat the same liquid (L) is present in both.

FIG. 4 shows an embodiment which provides that the prism (P) andintermediate element (IE) are merged and of single piece construction.This system results in the prism (P) and second (2) element of FIG. 2are physically merged.

FIG. 5 shows a general ellipsometer system. A source of electromagneticradiation (LS) provides a beam of electromagnetic radiation which iscaused to pass through a polarizer (POL) enter and exit the prism (P),pass through an analyzer (ANL) and enter a detector (DET). A compensator(COM) is also shown. In use any of the elements (POL), (COM) or (ANL)can be caused to rotate.

Note also that FIGS. 1-4 indicate that, as indicated in dashed lines,the prism can be replaced with a half sphere or half cylinder. Theimportant point being that electromagnetic radiation can enter and exitalong a locus which is perpendicular to the surface thereof. Theidentifier “P” should be interpreted to identify curved or straightintersecting sides.

Having hereby disclosed the subject matter of the present invention, itshould be obvious that many modifications, substitutions, and variationsof the present invention are possible in view of the teachings. It istherefore to be understood that the invention may be practiced otherthan as specifically described, and should be limited in its breadth andscope only by the Claims.

1. A system for use in investigating optical properties of a liquidcomprising: a prism element comprising first, second and thirdsubstantially flat sides, the second side of which is extended laterallybeyond projected meeting points with the first and third sides; a secondelement comprising closed sides and top and an open bottom; thelaterally extended second side of said prism being placed intofunctional contact with said second element at the bottom thereof toform a liquid containing cavity; such that leakage of liquid, whichliquid is caused to be present in said liquid containing cavity, doesnot occur through said contact point; such that in use liquid is causedto be present in said liquid containing cavity and electromagneticradiation is caused to enter said first or third side of said prism,interact with said second side thereof, and totally internally reflectthrough said third or first side thereof, respectively.
 2. A system asin claim 1, which is rotated to orient the open bottom to face otherthan downward.
 3. A system for use in investigating optical propertiesof a liquid comprising: a prism comprising first (1st), second (2nd) andthird (3rd) substantially flat sides; an intermediate element (IE); athird (3) element comprising closed sides and top and an open bottom;wherein said second (2nd) side of said prism (P) is affixed to saidintermediate element (IE) by substantially stress free means, andwherein said intermediate element (IE) when placed into contact with thebottom of said third (3) element forms a liquid (L) containing cavity (3c), said third (3) element and intermediate element (IE) being forcedinto functional contact with one another such that leakage of liquid(L), which liquid is caused to be present in said liquid containingcavity (3C), does not occur through said contact point; such that in useliquid can be caused to be present in said liquid containing cavity (3C)and electromagnetic radiation can be caused to enter said first (1st) orthird (3rd) side of said prism (P), interact with said second (2nd) sidethereof, totally internally reflect and exit through said third (3rd) orfirst (1st) side thereof.
 4. A system and in claim 3 in which saidintermediate element comprises a cavity sequestered therewithin.
 5. Asystem as in claim 4, in which said intermediate element cavity isfilled with a fluid.
 6. A system and in claim 3 in which the cavity ofthe intermediate element is continuous with the liquid containing cavityof the third element.
 7. A system as in claim 3 in which the prism andintermediate element are of single piece construction.
 8. A system as inclaim 3, which is rotated to orient the open bottom to face other thandownward.
 9. A system for use in investigating optical properties of aliquid comprising: a half sphere or half cylinder element comprising afirst curved and second substantially flat side, the second side ofwhich is extended laterally beyond the points of intersection of firstcurved side; a second element comprising closed sides and top and anopen bottom; the laterally extended second side of said half sphere orhalf cylinder being placed into functional contact with said secondelement at the bottom thereof to form a liquid containing cavity; suchthat leakage of liquid, which liquid is caused to be present in saidliquid containing cavity, does not occur through said contact point;such that in use liquid is caused to be present in said liquidcontaining cavity and electromagnetic radiation is caused to enter saidfirst curved side of said half sphere or half cylinder, interact withsaid second side thereof, totally internally reflect therefrom and exitthrough said first curved side thereof, respectively.
 10. A system andin claim 9 in which said intermediate element comprises a cavitysequestered therewithin.
 11. A system and in claim 9 in which the cavityof the intermediate element is continuous with the liquid containingcavity of the third element.
 12. A system as in claim 9 in which thehalf sphere or half cylinder and intermediate element are of singlepiece construction.
 13. A system as in claim 9, which is rotated toorient the open bottom to face other than downward.
 14. A system for usein investigating optical properties of a liquid comprising: a halfsphere or half cylinder comprising first (1st) curved and second (2nd)substantially flat side; an intermediate element (IE); a third (3)element comprising closed sides and top and an open bottom; wherein saidsecond (2nd) substantially flat side of said half sphere or halfcylinder (P) is affixed to said intermediate element (IE) bysubstantially stress free means, and wherein said intermediate element(IE) when placed into contact with the bottom of said third (3) elementforms a liquid (L) containing cavity (3C), said third (3) element andintermediate element (IE) being forced into functional contact with oneanother such that leakage of liquid (L), which liquid is caused to bepresent in said liquid containing cavity (3C), does not occur throughsaid contact point; such that in use liquid can be caused to be presentin said liquid containing cavity (3C) and electromagnetic radiation canbe caused to enter said first (1st) curved side of said half sphere orhalf cylinder (P), interact with said second (2nd) substantially flatside thereof, totally internally reflect therefrom and exit through saidfirst half sphere or half cylinder first (1st) curved side thereof. 15.A system as in claim 10, in which said intermediate element cavity isfilled with a fluid.
 16. A system as in claim 14, which is rotated toorient the open bottom to face other than downward.
 17. A method ofdetermining the optical properties of a liquid comprising the steps of:a) providing a system for use in investigating optical properties of aliquid comprising a selection from the group consisting of: a prismelement comprising first, second and third substantially flat sides, thesecond side of which is extended laterally beyond projected meetingpoints with the first and third sides; and a half sphere or halfcylinder element comprising a first curved and second substantially flatside, the second side of which is extended laterally beyond the pointsof intersection of first curved side; said system further comprising asecond element comprising closed sides and top and an open bottom; thelaterally extended second side of said prism, half sphere or halfcylinder element being placed into functional contact with said secondelement at the bottom thereof to form a liquid containing cavity, suchthat leakage of liquid, which liquid is caused to be present in saidliquid containing cavity, does not occur through said contact point;such that in use liquid can be caused to be present in said liquidcontaining cavity and electromagnetic radiation can be caused to entersaid first curved side of said half sphere or half cylinder element, orenter said first or third side of said prism, interact with said secondsubstantially flat side of said half sphere or half cylinder element orsaid prism, totally internally reflect therefrom and exit through saidfirst curved side of said half sphere or half cylinder element or saidthird or first side thereof, respectively; b) causing said liquidcontaining cavity to contain a liquid; c) causing electromagneticradiation to enter said first curved side of said half sphere or halfcylinder element or enter said first or third side of said prism,interact with said substantially flat second side thereof, totallyinternally reflect and exit through said curved side of said half sphereor half cylinder element or said third or first side thereofrespectively and enter a detector; d) analyzing data provided by thedetector in response to the electromagnetic radiation that entersthereinto to the end that optical properties of the liquid aredetermined.
 18. A method as in claim 17, which comprises an additionalstep comprising rotating the system to orient the open bottom to faceother than downward.